1. Field of the Invention
The present invention relates to a scanner, an image forming apparatus, and a scanning method.
2. Description of the Related Art
Such a scanner has been known that scans a photoconductor and the like with a light beam while controlling emission of the light beam output from a light source such as a semiconductor laser diode (LD) based on a dot of each pixel composing image data.
With such a scanner, techniques have been known that, if a target dot has a neighboring dot, move the target dot close to the neighboring dot and make successive dots (for example, see Japanese Patent Application Laid-open No. 2013-175851).
Laser diodes, however, take a time to light and to output a light beam after current is applied thereto (in other words, an oscillation delay is caused). If a target dot is an isolated dot without neighboring dots, the oscillation delay shortens the lighting time of the laser diode (the luminescent time of a light beam) by the amount of the oscillation delay. If the target dot is a successive dot, the laser diode continuously lights. The laser diode is therefore not affected by the oscillation delay, and the lighting time is less likely to be shortened.
As described above, even with an identical target dot, if a laser diode has a different lighting time depending on whether the dot is an isolated dot or a successive dot, the difference affects the image quality.
For example, Japanese Patent Application Laid-open No. 2002-292929 describes a technique to modulate power and equalize the amount of exposure of a light beam between an isolated dot and a successive dot.
Such a conventional technique, however, does not solve the problem that, even with an identical target dot, a light source may have a different lighting time depending on whether the target dot is an isolated dot or a successive dot. This problem may cause a tone jump.
Therefore, it is desirable to provide a scanner, and an image forming apparatus, and a scanning method capable of improving the gradation of an image.